During the electrolysis of water, the water molecules are broken down into hydrogen (H2) and oxygen (O2) by electric current. In a fuel cell, inter alia this operation takes place in reverse. Electrochemical combining of hydrogen and oxygen to form water results in the formation of electric current with a high level of efficiency and, if the fuel gas used is pure hydrogen, without the emission of pollutants and carbon dioxide (CO2).
Technical implementation of the principle of the fuel cell has led to various solutions, specifically with different types of electrolytes and with operating temperatures of between 80° C. and 1000° C. Depending on their operating temperature, the fuel cells are classified as low-temperature, medium-temperature and high-temperature fuel cells. These are in turn different from one another by virtue of differing technical implementations.
For operation, operating media, such as for example the operating gases, humidification water and cooling water, are fed to a fuel cell. The operating gases used are a hydrogen-containing fuel gas and an oxygen-containing oxidation gas. Examples of the fuel gases which can be used include natural gas, coal gas or pure hydrogen, while the oxidation gas used is generally air or pure oxygen.
Humidification water is fed to some embodiments of low-temperature fuel cells, in particular fuel cells with a polymer electrolyte membrane (PEM fuel cells), the membrane of which has to be kept moist. In this case, the operating gases are heated in a suitable device, for example a liquid ring compressor or in humidifier cells, to the temperature of the fuel cell and saturated with steam.
A single fuel cell supplies an operating voltage of at most approximately 1.1 V. Therefore, a large number of fuel cells are connected up to form a fuel cell stack which forms part of a fuel cell block. Connecting the fuel cells in series makes it possible to achieve an operating voltage of a fuel cell block of 100 V and above.
In addition to at least one fuel cell stack, a fuel cell block generally also comprises a humidifying cell stack and what is known as an operating part, also known as the supply part. The humidifying cell stack includes a number of cells in which the operating gases are humidified with the aid of a membrane. The supply part accommodates units such as, for example, pumps, compressors and humidifiers, as well as equipment such as valves, sensors, electronic monitoring devices, water separators and more.
The units are connected up by a large number of lines and pipe connections. These pipe connections are fundamentally susceptible to leaks. In this context, leaks in lines which carry an operating gas represent a particular risk to operating safety, since the use of hydrogen-containing and oxygen-containing operating gases means that there is a risk of a fire and possibly even explosions around a leak. When a fuel cell block is being used in a vehicle, an additional difficulty is that the fuel cell block is subject to shocks and vibrations.